Pupil-to-teacher ratio is kept very small.

The highest number of students who work with one teacher in any of these early
intervention programs is seven. Programs such as Early Intervention in Reading
and the Boulder Project present evidence that many children can make significant
progress when instruction is given to small groups of students; however, there is
no question that one-to-one tutoring is the most powerful form of intervention
(Pinnell, et al., 1994; Wasik & Slavin, 1993). It seems highly likely that at
least some children who are encountering very serious problems in learning to
read will need the intense support of one-to-one tutoring. As yet, no one has
suggested guidelines for determining which students can respond to group
instruction and which require individual tutoring. It seems reasonable to begin
with group instruction for most students and to switch to individual instruction
for those students who are having difficulty making progress.